Nail and Skin Structure, Growth, and Disorders
The nail unit, the skin, and what may be worked on
Draw the nail unit from memory: nail plate (the hard keratin you file), nail bed (pink tissue beneath it), matrix (living tissue that produces the plate, whose visible front end is the lunula), cuticle or eponychium (dead tissue sealing the base), hyponychium (the seal under the free edge), lateral nail folds and nail grooves, and perionychium (skin around the nail).
Skin has three layers: epidermis (outermost, no blood vessels - the cuticle is dead epidermis), dermis (nourishes; holds nerves and vessels), and subcutaneous tissue. Questions test whether you can separate a condition you may work over from one you must refer.
Work over with care: onychophagy (bitten nails), onychorrhexis (split or brittle), leukonychia (white spots), onycholysis (separated plate - do not force), agnail or hangnail (trim, never pull), mild koilonychia, Beau's lines, and ordinary ridges.
Refer or refuse: paronychia (red, swollen, pus), inflamed onychocryptosis (ingrown), onychomycosis (thick, yellow, crumbling), tinea pedis, pseudomonas (green-black stain), any dark streak reaching the matrix, sudden onychomadesis, open wounds, and warts.
Traps: the lunula is matrix, not plate. The cuticle is dead tissue; the eponychium is living and is never cut. Nippers trim tags, not living skin. A green nail is bacterial, not fungal - questions often swap the two.
Rule of thumb: if tissue is red, swollen, painful, weeping, or changing color in a streak, it is not yours to treat - refer and document.